In recent years, a fiber-reinforced plastic material (hereinafter referred to as “FRP material”) has been used in various fields (e.g., automobile, construction, and ship). The FRP material is bonded to various materials. A urethane adhesive is normally used for the FRP material.
When bonding a resin material such as the FRP material, the surface of the resin material is generally subjected to a surface treatment (e.g., primer treatment or sanding treatment) in advance. Such a surface treatment improves the adhesive properties, adhesive strength, etc. of the resin material, but increases the number of production steps so that the production efficiency decreases. Therefore, an adhesive that exhibits excellent adhesive properties without applying a primer treatment or a sanding treatment has been desired.
For example, a two-part urethane adhesive composition that contains a first liquid that contains a polyisocyanate and/or a polyisocyanate prepolymer and a second liquid that contains two polyols that differ in number average molecular weight has been proposed (see Patent Document 1, for example).    Patent Document 1: JP-A-1-132674